Surfactant based gelling composition for wellbore service fluids

ABSTRACT

A composition, in particular a wellbore service fluid, comprising monomeric surfactants, preferably viscoelastic surfactants, in combination with a polymerization agent. Additionally, the fluid may contain a cross-linking agent to cross-link the polymerized surfactants.

The present invention relates to surfactant, particularly viscoelasticsurfactant based gelling compositions preferably used for wellboreservice fluids. More particularly it relates to such compositions forselectively reducing the flow of subterranean aqueous fluids into a wellwhile maintaining the hydrocarbon production.

BACKGROUND OF THE INVENTION

Various types of wellbore fluids are used in operations related to thedevelopment, completion, and production of natural hydrocarbonreservoirs. The operations include fracturing subterranean formations,modifying the permeability of subterranean formations, or sand control.Other applications comprise the placement of a chemical plug to isolatezones or complement an isolating operation. The fluids employed by thoseoperations are known as drilling fluids, completion fluids, work overfluids, packer fluids, fracturing fluids, conformance or permeabilitycontrol fluids and the like.

Of particular interest with regard to the present inventions are fluidsfor water control applications: During the life cycle of a hydrocarbonwell, e.g., a well for extracting oil or natural gas from the Earth, theproducing well commonly also yields water. In these instances, theamount of water produced from the well tends to increase over time witha concomitant reduction of hydrocarbon production. Frequently, theproduction of water becomes so profuse that remedial measures have to betaken to decrease the water/hydrocarbon production ratio. As a finalconsequence of the increasing water production, the well has to beabandoned.

In many cases, a principal component of wellbore service fluids aregelling compositions, usually based on polymers or viscoelasticsurfactants.

There has been considerable interest in the viscoelastic gels formedfrom the solutions of certain surfactants when the concentrationsignificantly exceeds the critical micelle concentration. Viscoelasticsurfactant solutions are usually formed by the addition of certainreagents to concentrated solutions of surfactants, which most frequentlyconsist of long-chain quaternary ammonium salts such ascetyltrimethylammonium bromide (CTAB). Common reagents which generateviscoelasticity in the surfactant solutions are salts such sodiumsalicylate and sodium isocyanate and non-ionic organic molecules such aschloroform. The electrolyte content of surfactant solutions is also animportant control on their viscoelastic behaviour. The viscoelasticproperties of a solution arises from the formation of long cylindrical(or “worm-like”) micelles and their entanglement to form athree-dimensional structure. The surfactant micelles behave in a mannersomewhat similar to polymer chains, although the former are dynamicentities with the surfactant monomers constantly joining and leaving themicelles. The micelles are held together by van der Waals (and othersimilar) interactions, in contrast to the strong covalent bonds betweenmonomer units in polymers. The surfactant micelles are fragile (4) andthe gels formed by the entangled micelles are relatively weak. Such gelsare often termed physical gels (6), in contrast to chemical gels whichare commonly formed by the cross-linking of high molecular weightpolymers using covalent or ionic bonds.

Further references related to the use of viscoelastic surfactants aswellbore service fluids can be found for example in U.S. Pat. No.4,695,389, U.S. Pat. No. 4,725,372, U.S. Pat. No. 5,258,137 and U.S.Pat. No. 5,551,516.

Several patents have described the use of polymerizable surfactants inemulsion polymerizatio. In U.S. Pat. No. 5,162,475, there is describedthe use of α-β (i.e., terminal) ethylenically unsaturatedpoly(alkyleneoxy) compounds which act as the surfactant in the emulsionpolymerization process and which co polymerize with the non-surfactantmonomers. Several earlier patents, U.S. Pat. No. 4,049,608, 4,224,455and 4,337,185 have also described the co-polymerization of thesurfactant monomers used in emulsion polymerization processes. In U.S.Pat. No. 4,064,091 there is described the use of unsaturated quaternaryammonium salts as surfactants in emulsion polymerization processes whichco-polymerize with the non-surfactant monomers to produceself-stabilising polymeric dispersions which are free of surfactantmonomers.

Most recent work by K. Tauer, published in “Polymeric Dispersions:Principles and Applications” (J. M. Asua ed.), NATO ASI Series E:Applied Sciences Vol. 335, 1997 describes the polymerization ofsurfactant-like monomers in small micelles in the absence of othersurfactants.

The object of this present invention is to provide improvedcompositions, especially or wellbore service fluids, based on monomericsurfactants, particularly monomeric viscoelastic surfactants. It is aspecific object of the invention to provide stable gels using suchcompositions. It is a further specific object of the invention toprovide such compositions for water control operations in hydrocarbonwells.

SUMMARY OF THE INVENTION

The objects of the invention are achieved by polymerizing monomericsurfactants forming micelles in an aqueous solution.

Herein, monomeric is defined as having no repetitive units. Preferably,the molecular mass of monomeric surfactants is less than 10000,preferably less than 1000 units.

Surfactants are water soluble surface-active materials with ahydrophobic group. The solubility in water is controlled by ahydrophilic group. Surfactants are usually classified according to theirelectrochemical properties as anionic, cationic or non-ionic agents.Often they are referred to as detergents, soaps or amphiphiliccompounds.

In solution (and above a critical concentration) surfactants formmicelles. The concentration of the surfactants is sufficient totransform the solution into a gel. Preferably, the concentration lies inthe range of 1 to 10 weight per cent.

In a preferred embodiment of the invention the momomeric surfactantbelong to the class of surfactant which display in solution viscoelasticbehavior.

The polymerizing agent is capable of initiating a polymerization of thesurfactants forming a micelle, thus stabilizing the gel.

The concentration of the agent is preferably in the range of 10 to 1000ppm (parts per million)

As applied to solutions, the term “viscoelastic” means a viscoussolution which at least partially returns to its original state when anapplied stress is released. The property of viscoelasticity can betested for example by observing whether bubbles created by swirling thesample recoil after the swirling ceased. For this and other testreference is made to H. A. Barnes et al. Rheol. Acta. 14 (1975), pp.53-60 and S. Gravsholt, Journal of Coll. and Interface Sci. 57(3), 1976,pp.575-6.

The physical gels formed by viscoelastic surfactant solutions canexhibit considerable responsiveness to their external chemical andphysical environments. For example, the viscoelasticity of theseconcentrated surfactant solutions can be destroyed by contact withhydrocarbons and other organic liquids. The viscoelasticity of thesolutions can also be lost on heating but recovered on cooling. However,once polymerized, the polymeric gels formed show significantly lessresponsiveness to their chemical and physical environment. Viscoelasticsurfactants employed by the current invention are described for examplein the above cited U.S. Pat. No. 4,695,389, U.S. Pat. No. 4,725,372, andU.S. Pat. No. 5,551,516 and literature referred to therein.

In a further preferred embodiment of the invention, the polymerizedsurfactants are cross-linked, thus further enhancing the stability ofthe gel. The preferred concentration of the cross-linking agent in thesolution lies in the range of 10 to 1000 ppm.

Chemical cross-linking is defined as forming a chemical bond between thecross-linked molecules. Chemical cross-linking is understood to bestable and irreversible.

The cross-linking agents can be either inorganic ions (or ioniccomplexes) or polar organic molecules. When the polymer contains ionicgroups such as carboxylate or sulphonate functions the polymer chainscan be cross-linked by inorganic ions such as chromium(III) orzirconium(IV), frequently in the presence of monomeric ligands, such asacetate or adipate ions, to control the rate of cross-linking.Alternatively, organic cross-linking agents, such as hexanal orheptanal, can be used.

These and other features of the invention, preferred embodiments andvariants thereof, and further advantages of the invention will becomeappreciated and understood by those skilled in the art from the detaileddescription following below.

MODE(S) FOR CARRYING OUT THE INVENTION

The polymerization and cross-linking of the cylindrical micelles inviscoelastic surfactant solutions is illustrated with three examples.The polymerization in the three examples is achieved by a free radicalmechanism. However, it is stressed that the polymerization of thesurfactant monomers to form polymeric surfactants can be achieved by anumber of well known methods, including ring-opening polymerization,cation polymerization and anionic polymerization techniques. Adescription of these and other polymerization techniques has been givenby G. Odian in: “Principles of Polymerization”, 3rd ed., pp., Wiley,N.Y. (1991).

EXAMPLE 1

The first example is the polymerization of the surfactantN-erucyl-N,N-bis(2-hydroxyethyl)-N-methylammonium chloride

in an aqueous solution. The polymerization of the surfactant moleculesis achieved by joining the carbon-carbon double bonds by a free radicalpolymerization reaction within the micelles using the followingprocesses.

A viscoelastic surfactant solution was produced using 30 g/l of thesurfactant N-erucyl-N,N-bis(2-hydroxyethyl)-N-methylammonium chloridewith 40 g/l ammonium chloride. A volume of 100 ml of the viscoelasticsurfactant solution was placed in a bottle which was purged with drynitrogen gas to remove any dissolved oxygen. After sufficient purging 10mg of the free radical initiator2,2′-azo(bis-amidinopropane)dihydrochloride was added to theviscoelastic surfactant solution and mixed thoroughly.

The surfactant solution was heated at 60° C. for 24 hours under anatmosphere of nitrogen. Polmerization of the surfactant monomers ingiant micelles resulted in the viscosity of the gel becoming insensitiveto contact with hydrocarbon. The viscosity of the surfactant gel was notaltered by polymerization of the surfactant monomers. The polymerizedsurfactant gel retained its gel strength after prolonged contact withwater.

EXAMPLE 2

The second example is the polymerization of the viscoelastic surfactantsolution formed by potassium oleate in a potassium chloride electrolytesolution:

The viscoelastic surfactant solution was formed by mixing 60 g/lpotassium oleate with 60 g/l potassium chloride. A sample of 100 ml ofthe viscoelastic surfactant solution was purged with nitrogen and mixedwith 10 mg of the initiator 2,2′-azo(bisamidinopropane)dihydrochloride.The solution was heated at 60° C. for 24 hours under an atmosphere ofnitrogen. The resulting solution of polymerized surfactants was slightlyless viscoelastic than the original monomeric solution but the observedviscoelasticity was insensitive to contact with hydrocarbon. The gelformed by the polymerized surfactant retained its viscoelasticity afterprolonged contact with water

EXAMPLE 3

The third example is the polymerization of a long-chain vinylsurfactant, the potassium salt of 10,17-octadecyldienoic acid

in a viscoelastic solution. The surfactant monomer is synthesized by atwo stage reaction which involves coupling of the short-chain vinylsurfactant 10-undecenoic acid to 8-bromo-1-octene. The first stageconsists of reacting the 10-undecenoic acid with ozone indichloromethane followed by treatment with dimethyl sulphide (DMS) at−78° C. to convert the carbon-carbon double bond to a terminal aldehydegroup by the so-called oxo-uncoupling reaction. The second stageconsists of reacting the 8-bromo-1-octene with triphenylphosphine indichloromethane to form 8-triphenylphosphonium-1-octene bromide which isthen coupled with the aldehyde carboxylic acid and butyllithium intetrahydrofuran by the Wittig reaction to form the surfactant monomer asshown above.

The potassium salt of 10,17-octadecyldienoic acid forms a viscoelasticsurfactant solution at a concentration of 60 g/l in the presence of 40g/l ammonium chloride. The surfactant monomers were polymerized using 10mg of the free radical initiator2,2′-azo(bis-amidinopropane)dihydrochloride in 100 ml of viscoelasticsurfactant solution which had been purged with nitrogen gas. Thesolution was heated at 60° C. for 24 hours under an atmosphere ofnitrogen.

Polymerization of the surfactant resulted in a rigid gel which retainedthe viscoelasticity of the original (monomeric) surfactant solution butshowed none of its sensitivity to contact with hydrocarbon or water.

In all three of the examples given above it is possible to cross-linkthe polymeric micelles to increase the gel strength and to reducefurther any sensitivity of the gel to its chemical and physicalenvironment. The carboxylated polymers shown in the three above examplescan be cross-linked using a polyvalent metal ion, such as chromium(III)or zirconium(IV) ions. Similarly, if the terminal carboxylate groups arereplaced by sulphonate groups, then the polymerized micelles can also becross-linked with metal ions such as zirconium(IV). Alternatively, theoriginal viscoelastic surfactant solution can be composed of twodifferent types of surfactant monomer which form mixed cylindricalmicelles. The second surfactant monomer can be chosen to give a requiredcross-linking functionality to the polymerized micelle. For example, aviscoelastic surfactant solution can be formed with10,17-octadecyldienoic acid and its amide 10,17-octadecyldienamide addedin the mole fraction ratio of approximately 0.98:0.02. The twosurfactants can be polymerized, as in example 3 given above, to yield aco-polymerized micelle. The amide groups within the polymerized micellescan be used to cross-link them with organic cross-linking agents such asformaldehyde and phenol. The high concentration of surfactant in theaqueous solution can be used to solubilise otherwise insolublelong-chain cross-linking agents such as hexanal or octanal. Othercross-linking functional groups can be envisaged.

What is claimed is:
 1. A wellbore service fluid comprising an aqueoussolution of monomeric surfactants and a polymerization agent, whereinsaid monomeric surfactants are viscoelastic and said polymerizationagent is capable of polymerizing said monomeric viscoelastic surfactantsunder subterranean conditions.
 2. The fluid of claim 1, wherein thepolymerization agent is a radical, a cationic, or an anionic initiator.3. The fluid of claim 1 wherein the concentration of the monomericviscoelastic surfactants is sufficient to form micelles.
 4. The fluid ofclaim 1 wherein the concentration of the monomeric viscoelasticsurfactants is between 1 and 10 weight per cent.
 5. The fluid of claim 1wherein the monomeric viscoelastic surfactants form a gel.
 6. The fluidof claim 1, further comprising a cross-linking agent.
 7. Method offorming and stabilizing a gel comprising the steps of preparing and anaqueous solution of monomeric viscoelastic surfactants; adding to saidsolution a polymerization agent; injecting said solution into asubterranean wellbore; and letting said surfactants polymerize in thepresence of said polymerization agent.
 8. The method of claim 7, furthercomprising the steps of adding a cross-linking agent to the solution;and crosslinking the polymerized surfactants.
 9. The fluid of claim 1wherein said fluid is a viscoelastic gel before polymerization of themonomeric viscoelastic surfactants by the polymerization agent and saidfluid is a viscoelastic gel after polymerization of said monomericviscoelastic surfactants by said polymerization agent.
 10. The fluid ofclaim 9 wherein the gel before polymerization of the monomericsurfactants by the polymerization agent is responsive to hydrocarbonsand the gel after polymerization of said monomeric viscoelasticsurfactant by said polymerization agent displays a lower responsivenessto hydrocarbons than said gel before polymerization of the monomericsurfactants by the polymerization agent.
 11. The fluid of claim 9wherein the gel after polymerization of the viscoelastic monomericsurfactants by the polymerization agent displays an improved resistanceto the temperature as compared to the gel before polymerization of theviscoelastic monomeric surfactants by the polymerization agent.
 12. Thefluid of claim 3 wherein the concentration of the monomeric viscoelasticsurfactants is sufficient to form entangled worm-like micelles.
 13. Awellbore service fluid comprising an aqueous solution of viscoelasticsurfactants and a polymerization agent, said polymerization agent beingcapable of polymerizing said viscoelastic surfactants under subterraneanconditions, said fluid forming a viscoelastic gel before polymerizationof the viscoelastic surfactants by the polymerization agent and forminga viscoelastic gel after polymerization of said viscoelastic surfactantsby said polymerization agent.